This invention relates to the field of X-ray tubes, specifically tubes wherein a magnetic field urges electrons toward the anode.
X-ray sources have many applications. For example, hundred kilovolt X-ray tubes can be used in agriculture for de-infestation of fruits, vegetables, grains, and lumber. They can also be used to sterilize food for storage without refrigeration, and to destroy pathogenic microorganisms in meat, seafood, and poultry. They can also be used for non-destructive testing and inspection of industrial tools and systems (e.g., airplanes) and for water purification.
Many X-ray tubes consist of an electron source and an accelerating potential that impinges a beam of electrons onto an X-ray conversion target anode. The anode is typically made of a high atomic number material so that it efficiently decelerates the electrons that penetrate into it, thus generating Bremsstrahlung X-radiation. Many production processing applications require electron beams of only a few hundred kilovolts accelerating potential, so the X-ray pattern is substantially isotropic.
One common X-ray tube design involves a diode, wherein a heated cathode provides electrons and an applied voltage between the cathode and an anode accelerates the electrons onto the anode. Field shaping electrodes around the cathode can be used the create an accelerating electric field that will focus the electron beam onto the anode. A large part of the energy in the electrons can be converted into heat in the anode; some of the energy is carried away by electrons that miss or bounce off the target; the remaining small portion is converted into subsequently reflected from anode A1, they will carry away energy that might otherwise have further contributed to X-ray production. Radiation along directions other than through the window W1 can be absorbed by cathode C1, anode A1, and envelope E1, contributing to undesirable heating of tube T1 rather than to useful radiation of the target TG1.
Accordingly, there is a need for an improved X-ray tube that provides increased X-ray generation efficiency by reducing the number of electrons that do not contribute to X-ray production.